IPF, NAT or NIC problem

I'm new in BSD, I installed FreeBSD 7.2 and want to use as gateway with IPF and NAT. I have 2 NIC's fxp0 and rl0. When i booted up my pc i got a message "gateway kernel: arp xxx.xxx.88.17 is on fxp0 but got reply from rl0". My configuration files looks like this: